This retrospective cohort study was conducted in a large tertiary centre in South India with 14,759 deliveries between January and December 2016. The study was approved by the Institutional Review Board (IRB No.10601 {Retro} dated 29-03-2017). This facility from where records were obtained followed by evidence-based practices to the extent possible.

All women with WD that needed primary repair or managed conservatively with dressings resulting in secondary healing were included as cases. Controls were selected in a 1:2 fashion from the electronic register matched for delivery by the same route, same day and with the same team of doctors and midwives that did not have WD at discharge or at the six week postnatal visit. Women with intact perineum were excluded.

The use of prophylactic antibiotics just before the incision was followed for all cesarean deliveries [15], but authors did not use antibiotics for normal or instrumental delivery [16], unless there was a complication such as a sphincter injury or vaginal haematoma. Episiotomies were performed in almost 70-80% of cases, unlike most developed countries. Perineal hair was not shaved but clipped. Chlorhexidine skin preparation was used for cesarean sections [14] and benzalkonium chloride solution was used for skin preparations in vaginal deliveries. Episiotomy of vaginal tears was sutured using continuous sutures for vaginal mucosa and interrupted sutures for muscle. Skin was sutured with mattress sutures. Suture material used for episiotomies or vaginal tears was the absorbable 2-0 rapid vicryl, All cesareans were done by a Pfannenstiel incision [8]. Subcutaneous tissue, rectus sheath and uterus were opened by the blunt technique. Uterus was closed in two layers if it was the first cesarean section and in one layer when the woman wanted sterilisation with a previous cesarean section. Interrupted subcutaneous sutures were inserted if the subcutaneous tissue was more than two centimetres. Skin was sutured by mattress sutures or subcuticular sutures. Normal vaginal deliveries were conducted by midwives or house surgeons with one or more years of experience. Most operative vaginal deliveries were performed by registrars with three or more years of experience. Induction of labour was done using 25 μg of vaginal misoprostol or 50 μg of oral misoprostol at four hourly intervals.

This facility has a meticulous record keeping along with a register for all WD. This register was maintained by research assistants who visited both, the postnatal wards and the outpatient treatment room daily to find cases of WD that was managed either with primary suturing or with dressings. During the year 2016 there were 4,671 women who underwent cesarean section and 10,088 women who had vaginal deliveries. Among vaginal deliveries, 2,526 women had instrumental delivery. Authors have a high instrumental delivery rate of 26% unlike other countries [3]. Out of the instrumental deliveries, 36% were delivered by outlet forceps and the rest were delivered by low forceps or suction cups. All women delivered by an instrumental delivery had an episiotomy. Women were generally discharged on the second or third postnatal day after VD and third or fourth postnatal day after CD, in the absence of any maternal or neonatal complication. Most women had a six week postnatal checkup, the details of which were entered into the patient notes. Women with complications generally returned to the facility [8]. Antenatal and inpatient records were retrieved and all details were collated by the first author. Parameters assessed were, gestational age, parity, IOL, mode of delivery, indication for operative delivery, date of diagnosis of WD, potential risk factors etc.

Categorical variables were summarised using counts and percentages. Quantitative variables were summarised using median and IQR. Mann-Whitney U-test was used to compare the medians between two groups. Chi-square test was used to compare the proportions between the groups. The predictors were determined using adjusted and unadjusted logistic regression. For all the analysis, 5% level of significance was considered to be significant.

The number of WD following 10,088 vaginal deliveries was 86 (0.8%). The baseline characteristics have been presented in [Table/Fig-1]. Age of the woman, gestational age at delivery and BMI >30 kg/m² were similar in both cases and controls. There were significantly more primigravidae among the cases when compared to controls. Among the potential antepartum and intrapartum risk factors in women with perineal wound dehiscence, anaemia in the antenatal period was more common among controls and this was statistically significant [Table/Fig-2a]. More number of women had IOL in cases compared to controls. Meconium stained amniotic fluid; instrumental delivery and episiotomy were also more common among cases when compared to controls. Third degree tear was more common among controls and this was statistically significant. However, multivariate analysis did not reveal IOL as an independent risk factor [Table/Fig-2b]. BMI >30 kg/m² and anaemia were more common in controls on multivariate analysis. Median duration of hospital days (IQR) with women who delivered vaginally was 7.5 (5,10) days in cases and 4 days (3,5.5) in controls and this was statistically significant {OR 1.63 (1.42,1.88) p≤.001}. 22 cases (25.5%) who delivered vaginally were given antibiotics while 3 controls (1.7%) were given antibiotics empirically. Of the women on antibiotics (n=22) one third were given ampicillin, gentamycin and metronidazole, another third were given Piperacillin, Tazobactam and metronidazole. Others were given ampicillin, gentamycin and metronidazole and upgraded to second line drugs i.e., Piperacillin, Tazobactam and metronidazole.

The number of WD following CD was 94 (2%). The baseline characteristics are presented in [Table/Fig-3]. Age of the woman and the gestational age at delivery were similar in cases and controls. Significantly more number of primis were seen in cases when compared to controls. BMI >30 kg/m² was significantly more common among cases as compared to controls. Women with previous LSCS were significantly more common among controls. Among the antenatal and intrapartum risk factors, hypertensive diseases and IOL were significantly more common among cases as compared to controls. This association was not seen in multivariate analysis [Table/Fig-4a,b]. Median duration of hospital stay in cases who delivered by CD was 6 days (5,12) and 5 days (4,7) in controls. This was also statistically significant {OR 1.27 (1.17,1.38) p≤001}. Post CD antibiotics was given in 50 of cases (52.63%) and only 20 controls (10.52%) p=.002. of cases in the women who needed antibiotics 30% were given ampicillin, gentamycin and metronidazole and another 30% were given Piperacillin, Tazobactam and metronidazole and the rest were given sequential antibiotics i.e., first started with ampicillin, gentamycin and metronidazole which was subsequently upgraded to Piperacillin, Tazobactam and metronidazole. Meropenen was used in only one case in each of the deliveries.

The present study found a WD rate of 0.8% following VD as seen in other studies [1]. One of the salient findings of this study was that IOL was significantly more common among cases when compared to controls in women who delivered vaginally. Meconium-stained amniotic fluid was more common among cases and this could be related to the long labour and the use of misoprostol with IOL [17]. WD was significantly more common with instrumental delivery and episiotomy as seen with other studies [3]. However, multivariate analysis did not show IOL as an independent risk factor.

Among the women who had CD, 2% had WD and this was similar to other studies [2]. The salient findings in this group were that IOL and BMI more than 30 were significantly more common among the cases when compared to controls. Hypertensive diseases were more common among cases as seen in an earlier study [18] and this could be related to the fact that IOL is more common in women with hypertensive disease. The association of induction of labour and WD has been described in only few studies [19]. Association of WD and BMI >30 kg/m² following CD has been described in several other studies [20]. However, association of IOL and BMI >30 kg/m² with WD in cases of CD were not seen in multivariate analysis in the present study. In both modes of delivery, primi gravida was more common among cases and this could be attributed to the fact that most multi-gravida has a short and easy intrapartum period with a decreased need of episiotomy or with decreased incidence of vaginal tears. Authors had some surprising findings in the present study some of which were misleading and related to the small sample size. For example, significantly more controls who had CD had anaemia in the antenatal period compared to cases of WD [21]. Authors found a high rate of third degree tears in controls which were 23.6% of all deliveries unlike 9% described in other centres [22]. More women with previous cesarean sections were found in controls and this was also an unusual finding. On multivariate analysis, BMI >30 kg/m² was found to protect WD in cases of VD. Since, this is not biologically plausible or coherent; this unusual finding can be attributed to the small sample size.

WD generally develops within 4 to 7 days after cesarean delivery [4,23]. The organisms causing SSI is usually A or B beta-hemolytic streptococcus or genital mycoplasm as [23,24]. These WD is not always treated with antibiotics after the wound is opened up since not all wounds are infected [22]. Antibiotics are indicated only in cases with cellulitis [25]. Postnatal hospital stay and antibiotic therapy in both modes of delivery were as expected in all cases of WD when compared to controls in the present study.

The strength of present study was that data was collected from a register that had information documented meticulously. However, as with any retrospective study, there are several limitations. Even though most women returned to present institution in the event of a complication, there may be under reporting especially of WD that occurs after discharge. Peripartum WD is more common with IOL. WD with VD was associated with meconium stained amniotic fluid, instrumental delivery and episiotomy. WD with CD was also associated with BMI more than 30. Careful assessment of indication for IOL is vital and is necessary to decrease the incidence of WD. Women who are obese or are undergoing IOL should be counselled in detail about the increased chance of WD.

An association between IOL, primigravidae, instrumental delivery and MSAF was seen with peripartum WD.